i currently have 2jd, 1 fm, 1 fh, 2con, 1 gt in the same tank. The cons will go after anyone near their babies but other than that nothing. there is a little chasing every now and then but nothing major. i would have to say right now my FH is the lowest one on the totem poll. hes about 4" and runs from my 2" FM. i will be seperating fish when my other tanks, 55g and 29g, are set up again.